Thermochemical hydrogen produced from a vanadium decomposition cycle

ABSTRACT

A thermochemical water-splitting process all reactions of which operate at relatively low temperatures and high efficiencies, and in which relatively inexpensive materials and processing methods are made possible. This invention involves the decomposition of a metal halide compound, i.e., one which is capable of being reduced from a higher oxidation state to lower oxidation state, e.g. vanadium chloride III→vanadium dichloride. The process is cyclic and regenerative, and the only net inputs are water and heat; and the only net outputs are hydrogen and oxygen. The process makes it possible to utilize a wide variety of available heat, including solar, sources for the energy input.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/868,257, now U.S. Pat. No. 7,799,315, filed Jun. 14, 2004, whichclaims the benefit of U.S. Provisional Application Ser. Nos. 60/477,499filed on Jun. 11, 2003; 60/552,431 filed on Mar. 11, 2004; and60/556,191 filed on Mar. 25, 2004, respectively, each of which isincorporated herein by reference in its entirety.

The present invention relates to a thermochemical water-splittingprocess all reactions of which operate at relatively low temperaturesand high efficiencies, and in which relatively inexpensive materials andprocessing methods are made possible. This invention involves thedecomposition of a metal halide compound, i.e., one which is capable ofbeing reduced from a higher oxidation state to lower oxidation state,e.g. vanadium chloride III→vanadium dichloride. The process is cyclicand regenerative, and the only net inputs are water and heat; and theonly net outputs are hydrogen and oxygen. The process makes it possibleto utilize a wide variety of available heat, including solar, sourcesfor the energy input.

BACKGROUND OF THE INVENTION

Perhaps the most studied thermochemical water-splitting process is knownas the sulfur-iodide process which operates at about 1000° C. This hightemperature requirement cannot be reached economically with current-artconcentrating solar thermal technologies, and does not allow thepractical harvesting of thermal energy from other resources such aswaste heat from turbines, low-quality combustible gases, and the like.Moreover, a process such as the Iodine-Sulfur process (I—S) operateswith extremely corrosive materials. The expense of dealing withcorrosion problems, as well as loss of a material as expensive asiodine, constitute significant drawbacks to using such a process.

Known low temperature processes, such as a copper chloride cycle requirethe use of silver chloride in its hydrogen cycle. Silver chloride isvery expensive, and further, the silver must be removed and reprocessedin order to recover it. In a real world plant this fact alone guaranteesunacceptable loses of silver. With silver at $80 per pound ($5.70/TrOz), and twice the molar requirement per mole of product hydrogen, theinitial capital cost is commercially unacceptable. Moreover, it ispossible that the silver losses alone could exceed the value of hydrogenproduced.

Considerable interest in thermochemical water splitting cycles was shownin the 1960's and 70's when it was thought that heat from a nuclearreactor would be the source of energy and systems that had at least onehigh temperature step were widely explored. However, the practicality ofusing a nuclear power plant for the purpose of making hydrogen did nottake into account the other more profitable uses of that heat.Furthermore, nuclear power has steadily fallen out of favor in the U.S.A key factor that was over-looked was the high temperatures requiredpresented serious problems including the use of construction materials.This alone doomed most of the proposed systems. While the prospect ofutilizing a high temperature seemed promising insofar as it could openthe door to many reactions and possibly high rates, after examination ofmany potential cycles, the flaws which inherent in them became all tooapparent, and none have been commercialized.

It is an object of the present invention to chose selectively, scaleablereactions at as low a temperature as possible to achieve a truly usefulprocess that can utilize, among other sources, waste heat and therebyincrease the efficiency of many energy sources as well as produceinexpensive hydrogen and oxygen.

SUMMARY OF THE INVENTION

According to the process of the present invention relatively low thermalenergy, preferably less than about 600° C. is used to decompose, e.g.,vanadium trichloride to vanadium dichloride and chlorine gas. Thechlorine gas is reacted with steam to produce oxygen and HCl (sometimescalled the “Reverse Deacon” reaction). The oxygen product and HCl areseparated, and the equilibrium shifted by incorporating an acidabsorbing material in the Reverse Deacon reactor for example byscrubbing with an acid-absorbing compound such as monoethanolamine. HClis liberated from the monoethanolamine by heating, and is then reactedwith the vanadium dichloride to produce hydrogen and vanadiumtrichloride. Thus, the vanadium trichloride is ready to begin the cycleagain. Preferred embodiments of the present invention contemplate theuse of catalysts, and the use of a double-salt of vanadium chloride, theeffect of which enable the use of even lower temperatures in the firstreaction, i.e., temperatures even below about 425° C. While the presentinvention will be generally discussed herein in connection with thedecomposition of vanadium trichloride (VCl₃) and optionally an irontrichloride (FeCl₃) catalyst, other suitable metal halides and catalystswill be understood as useful in practicing the process of the presentinvention.

The process of the present invention, referred to as the “V-Process,”offers several key advantages. For example, the relatively lowtemperature of operation allows the process to utilize knownconcentrating solar thermal energy, and other plentiful and advantageousenergy sources, to make hydrogen. The low temperature also allows theuse of relatively inexpensive materials for construction of plantequipment, and increases reliability of operation. The V-Processutilizes fairly inexpensive materials in the reactions, which materialsare neither destroyed nor significantly lost in the process. Forexample, vanadium salts are relatively abundant and inexpensive. Theprocessing steps and separations involved in the V-Process are simple,straightforward, and while individually known in general, have neverbeen combined as in the V-Process for the generation of thermochemicalhydrogen for use in the applications discussed below.

It is estimated that the V-Process can create hydrogen from thermalinput at roughly 73% efficiency based on the lower heating value (LHV)of the product hydrogen, or 87% based on the higher heating value (HHV).If steam is available to feed the process instead of liquid water, thenthe efficiency can be raised to about 78% (LHV)/94% (HHV). When theprocess is integrated with energy input sources such as solarconcentrators at high thermal efficiency, the result is the conversionof sunlight to hydrogen with an overall efficiency several times higherthan the efficiency of photovoltaic modules integrated withelectrolyzers. For instance, an advanced “power tower” (solarconcentrator plant) integrated with the V-Process converts sunlight tohydrogen at an efficiency of about 34% (LHV, liquid water)/43% (HHV,steam). Higher efficiencies are possible using highly efficient solarconcentrator technologies, properly engineered to facilitateintegration. Thus it is believed that using the V-Process in combinationwith a large advanced future power tower concentrator facility, thathydrogen may be generated at a cost of less than $1.00 per kg.Nevertheless, the estimated cost of using solar technology which has anear-term availability is believed to be less than $2.00 per kg.

Due to the low operating temperature used in the V-Process, various heatsources and waste gases may be readily utilized as an energy inputsource. For instance, a significant proportion of the exhaust heat froma simple-cycle gas turbine power plant can be used. Even turbine exhaustheat well below 500° C. may still be useful in facilitating secondaryreactions in the V-Process. Using such a low-cost source of heat, it isestimated that hydrogen could be produced for less than $0.50 per kg.Other energy sources include flue gases, waste heat from any chemicalreactions wherein heat is available, foundry cooling processes, theburning of off-gases from a refinery and oil and natural gas wells, theintentional burning of lower BTU gases which produce a lower flametemperature than pure fuels, and the burning of any fuels for thepurpose of generating hydrogen and oxygen.

The low operating temperatures used in the V-Process also allows theproduction of hydrogen using the thermal energy byproduct from ahigh-temperature fuel cell, such as a solid oxide or molten carbonatefuel cell. Accordingly, an integrated process enables the V-Process tobe fed by solar or other suitable heat sources as a primary source ofthermal energy, as disclosed above; the hydrogen and oxygen from theV-Process itself can serve as fuel for a high-temperature fuel cell, thethermal energy from the fuel cell being “recycled” back to the V-Processto generate more hydrogen. The result is a highly efficient, and lowcost process for the production of electricity from solar thermal energyor other suitable heat sources.

The energy efficiency of the process of the present invention has beencalculated by performing a heat and material balance, and plant energybalance based on a conceptual process design shown schematically inFIG. 1. If the water fed to the process is in liquid form (so that itmust be vaporized within the process), the estimated efficiencies are:73% for the LHV of hydrogen product divided by total energy input; and87% for the HHV of hydrogen product divided by total energy input. Ifthe water fed to the process is steam (when the plant is integrated withanother process, or processes that can provide steam) the estimatedefficiencies are: 78% for LHV of hydrogen product divided by totalenergy input; and 93% for HHV of hydrogen product divided by totalenergy input. Concentrating solar thermal technologies generally rangein efficiency from about 45% efficiency to about 70% efficiency. If onemultiplies this by the V-Process efficiency at 73% (LHV, liquid H₂Oinput), the resulting efficiently of conversion of solar energy tohydrogen ranges from 33% to 51%. By contrast, the best commercialphotovoltaic modules coupled with the most efficient electrolyzers havesunlight to hydrogen conversion efficiency of about 14%.

The thermochemical hydrogen production process in accordance with thepresent invention is based on the liberation of hydrogen using a metalhalide in a cyclic, regenerative process which proceeds in three steps.As stated earlier, while the invention is hereinafter explained in thecontext of the initial thermal decomposition of vanadium trichloride,other suitable compounds may also be used. Accordingly, the first stepof the V-Process is the decomposition of vanadium trichloride tovanadium dichloride and chlorine. This reaction proceeds through anintermediate of vanadium tetrachloride, but the entire reaction takesplace in one vessel. The reaction is known in the literature to operatevery rapidly at 550° C. without any catalysts; however it has now beenfound that the reaction proceeds well below 500° C. and thermodynamiccalculations show that the thermal efficiency may well approach atemperature below 400° C. See FIGS. 6 and 7 (Graphs I and II,respectively). A suitable catalyst for this reaction, e.g., FeCl₃, mayfurther lower the temperature of this initial step. See FIGS. 8, 9, and10 (Graphs III, IV and V, respectively), in which FIG. 8 (Graph III)shows the catalytic effect of iron chloride (FeCl₃); FIG. 9 (Graph IV)provides a side-by-side comparison of the catalytic effect of FeCl₃ ascompared without the catalyst; and FIG. 10 (Graph V) makes a similarcomparison but uses a much slower heating rate, i.e. 2 C/min as shown inFIG. 7 (Graph II), versus 10° C./min.

The graphs are all generated on a TA Instruments TGA Model 2950Hi-Resolution Thermo-Gravimetric Analyzer. They show the amount ofweight loss of VCl₃ verses temperature. Since the decomposition of VCl₃produces a weight loss the progress of the reaction may be monitored byobserving weight loss. The TGA2950 samples weight twice per second. Thusthe line in the graph is composed of raw data points and not calculateddata. It can be seen from Graph (I) that at a 10° C./min heating ratethat the VCl₃ starts decomposition at around 275° C. and is done by 550°C. This is in agreement with the combined consensus of the availableliterature. However, in Graph III and IV, note the effect on thedecomposition temperature when FeCl3 is used as a catalyst. Note thatthe reaction starts at a lower temperature and stays ahead of itsuncatalyzed counter part until the reaction material is spent at 550° C.where the lines converge. See Graph IV. Clearly, FeCl3 is an effectivecatalyst for the decomposition of VCl₃. Note also in graph (II) that ifthe temperature ramp-up rate is lowered from the normally used 10° rateto a lower 2° rate that it can be seen more clearly that evenuncatalyzed the reaction commences at 150° C. and is complete at 360° C.Further, FeCl₃ still evidences a positive catalytic effect even at thismore accurate rate of increase of the temperature. Thus, it has beendiscovered that VCl₃ can be decomposed in the 300°-400° C. temperaturerange, which is over 100° C. lower than the known teaching of the priorart.

In a second step, halogen gas, i.e. the chlorine gas from the firstreaction is reacted with steam to produce oxygen and HCl (sometimescalled the “Reverse Deacon” reaction). In a third step, HCl is reactedwith the vanadium dichloride to produce hydrogen and vanadiumtrichloride. The vanadium trichloride is thus ready to begin the cycleagain.

In one embodiment of the V-Process, FIG. 2, the vanadium salts for boththe decomposition and regeneration steps are in a dry (powder) state.This process is as follows:

$\begin{matrix}\begin{matrix}{{2{VCl}_{3}} = {{2{V{Cl}}_{2}} + {Cl}_{2}}} & {525{^\circ}\mspace{14mu}{C.}} & {{{delta}\mspace{14mu} H} + 291} & {\mspace{79mu}(1)} \\{{{Cl}_{2} + {H_{2}O}} = {{{Co}\mspace{14mu}{cat}} = {{2{HCl}} + {\frac{1}{2}O_{2}}}}} & {100{^\circ}\mspace{14mu}{C.}} & {{{delta}\mspace{14mu} H} + 33} & {\mspace{34mu}(2)} \\\underset{\_}{{{2{VCl}_{2}} + {2{HCl}}} = {{2{VCl}_{3}} + H_{2}}} & {300{^\circ}\mspace{14mu}{C.}} & {{{delta}\mspace{14mu} H} + {- 7}} & {\mspace{34mu}(3)} \\{{{H_{2}O} + {heat}} = {H_{2} + {\frac{1}{2}O_{2}}}} & ({net}) & {{- 287}\mspace{14mu}{kJ}\text{/}{mole}} & \;\end{matrix} & \;\end{matrix}$All temperatures reported in the equations are illustrative only, andother suitable starting temperatures are indicated in Graphs I-IV,depending on the presence or absence of a catalyst.

Another embodiment of the V-Process, FIG. 3, is referred to as the “wetprocess.” The difference here is that the wet process releases hydrogenfrom an aqueous solution, thus allowing for a substantial simplificationof separation requirements. It also allows the use of very lowtemperature heat input for a portion of the process' energy needs,thereby improving the economy of the process where such low-grade heatis available. The “wet process” is as follows:

$\begin{matrix}\begin{matrix}{{2{VCl}_{3}} = {{2{VCl}_{2}} + {Cl}_{2}}} & {> {525{^\circ}\mspace{14mu}{C.}}} & {{{delta}\mspace{14mu} H} = {+ 291}} & {\mspace{20mu}(4)} \\{{{2{VCl}_{2}} + {2{HCl}_{({aq})}}} = {{2{VCl}_{3{({aq})}}} + H_{2}}} & {30{^\circ}\mspace{14mu}{C.}} & {{{delta}\mspace{14mu} H} = {- 17}} & (5) \\\; & \mspace{11mu} & \left( {{{dry}\mspace{14mu}{VCl}_{3}} = {+ 33}} \right) & \; \\\underset{\_}{{{Cl}_{2} + {H_{2}O}} = {{{Co}\mspace{14mu}{cat}} = {{2{HCl}} + {\frac{1}{2}O_{2}}}}} & {300{^\circ}\mspace{14mu}{C.}} & {{{delta}\mspace{14mu} H} - 12} & (6) \\{{{H_{2}O} + {heat}} = {H_{2} + {\frac{1}{2}O_{2}}}} & ({net}) & {{- 287}\mspace{14mu}{kJ}\text{/}{mole}} & \;\end{matrix} & \;\end{matrix}$

In the wet process the only extra step that is required is to dry thevanadium trichloride solution to anhydrous vanadium trichloride so thatit may be recycled for decomposition. This step is done in the presenceof hydrogen chloride gas, which does require the consumption of energy.However, the advantage of the wet process is that there is no need toseparate hydrogen chloride from oxygen. In facilities where low gradesteam (100°-200° C.) is available, as well as a higher temperature heatsource, the energy balance may well tip in favor of the wet process asthis heat (steam) can be used to dry the VCl₃ for reuse. However, ifexcess steam is not available, then the dry process will possibly bemore efficient. An engineer designing the V-Process thus has theflexibility of utilizing a suitable amount of energy by selecting thetype of V-Process (dry/wet) that is most compatible with the availableenergy (heat) source.

A variant of the V-Process is shown in FIG. 4 wherein another metalchloride salt is used to form a double salt. For instance, the additionof sodium chloride forms the compound NaVCl₄. This compound has theadvantages that it decomposes without going through the intermediate ofVCl₄, and that the decomposition temperature is narrower. The use ofdouble salts also offers the possibility of lowering the decompositiontemperature through the incorporation of less stable metal halide saltssuch as iron chloride. While the double salt process may be incorporatedinto the initial step (1) of either the wet or dry process, it stillutilizes a vanadium III/vanadium II cycle. An example of the double saltreaction is as follows:NaVCl₄→NaVCl₃+½Cl₂   (7)NaVCl₃+HCl→NaVCl₄+½H₂   (8)

As it can be seen, reactions 7 and 8 can replace, e.g. reactions 1 and 2in dry process. This sequence also eliminates any occurrence of VCl₄, avolatile intermediate of reaction (1).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a continuous process according to one embodiment of thedisclosed subject matter;

FIG. 2 depicts a continuous process according to one embodiment of thedisclosed subject matter;

FIG. 3 depicts a continuous process according to one embodiment of thedisclosed subject matter;

FIG. 4 depicts a continuous process involving a double salt according toone embodiment of the disclosed subject matter; and

FIG. 5 depicts a process according to one embodiment of the disclosedsubject matter.

FIG. 6 depicts a thermal decomposition curve of vanadium trichloride ata heating rate of 10° C./mm. in the absence of a catalyst;

FIG. 7 depicts a thermal decomposition curve of vanadium trichloride ata heating rate of 2° C./mm. in the absence of a catalyst;

FIG. 8 depicts a thermal decomposition curve of vanadium trichloride ata heating rate of 10° C./mm. in the presence of a FeCl₃ catalyst;

FIG. 9 depicts a side-by-side comparison of a thermal decompositioncurve of vanadium trichloride in the absence a catalyst, and a thermaldecomposition curve of vanadium trichloride in the presence of a FeCl₃catalyst, respectively, each at a heating rate of 10° C./mm.;

FIG. 10 depicts a side-by-side comparison of a thermal decompositioncurve of vanadium trichloride in the absence a catalyst, and a thermaldecomposition curve of vanadium trichloride in the presence of a FeCl₃catalyst, respectively, each at a heating rate of 2° C./mm.

DETAILED DESCRIPTION OF THE INVENTION

A particular preferred embodiment of the V-Process begins with reductionof vanadium chloride (III) to vanadium chloride (II) by decompositionwith heat. This reaction releases free chlorine gas from a firstreactor, and leaves behind solid vanadium II salt. The chlorine that isliberated from the vanadium salt may contain some VCl4, which can beremoved by simple condensation and returned to the beginning of the VCl3decomposition reactor used at the beginning of the V-Process.Thereafter, the chlorine is pure and requires no further cleaning priorto going to a second reactor. A catalyst, such as FeCl₃, may be used inthe initial reaction, the effect of which is to lower the temperature atwhich the VCl₃ is decomposed. See Graphs (III-V). Other suitablecatalysts include PbCl₄, SbCl₅, CrCl₄, MnCl₄, CoCl₃, K NiCl₄; N1Cl₃, andBiCl₅, FeCl₃, CuCl₂ and any other compounds that can reversibly absorb ahalogen gas. The choice of catalyst must be consistent with thecorresponding metal halide that is used in the initial reaction, e.g.VI₃ and PbI₄, or VBr₃ and PbBr₄.

The V-Process can be designed for batch-wise processing so that thevanadium salt solids stay in one reactor, while all mass transfers arecarried out by gas HCl, Cl₂, H₂, O₂ and water vapor. The process onlyrequires two solid bed reactors, an absorber, and a gas separationchamber. Alternatively, the process can be designed to be continuous, sothe VCl₃ moves through one reactor decomposing to VCl₂ and releasingchlorine, and then through another reactor to react with the HCl to formhydrogen. The solids may be conveyed through the reactors by a screwconveyor or pneumatically by a recycle loop of the reactant gases. Theconceptual, schematic process drawing in FIG. 1 shows a continuousprocess scheme using screw conveyors in the vanadium reactors.

As shown in FIG. 1, the chlorine that is generated is sent to a secondreactor where it is reacted with steam over a solid catalyst to generateHCl and O₂ according to reaction (2). The HCl and O₂ are separated fromeach other. The O₂ is a product of the process and the HCl is sent tothe first reactor to complete the cycle by generating hydrogen andregenerating the vanadium chloride III salt.

The oxygen and HCl are easily separated since HCl is acidic and verywater-soluble while oxygen is neither. One known industrial method thatis cost effective is to use a mildly basic material that absorbs the HClin a scrubber. The material is then sent to a second chamber where heatis applied and the HCl is recovered again as a gas and the base materialreused. Compounds such as monoethanolamine, diethanolamine,triethanolamine, melamine, zeolites, charcoals, silicas, alumina,magnesia and compounds having functionality that can reversibly absorban acid gas, such functionalities being for example NH₃, NH₂, OH, O, andC═C, for example, are suitable for this purpose. Water is also suitable,and a distillation set-up can be used to separate the two. This,however, would be more capital intensive than the simple scrubber—heatercombination described above; nevertheless if low grade waste steam isavailable the cost of running a still may be acceptable. Again theV-Process allows the engineer many design choices.

Further, any material that will absorb acidic gases such as HCl andwhich can be regenerated by heat is suitable. Many polymers that haveactive amine groups such as Melamine or poly-vinyl-pyridine type family,etc. can be used in accordance with the general equations:MEA(1)+Cl2(g)+H2O→deacon catalysts→MEA*HCl(s)+O2(g)   (9)MEA*HCl(s)→200° C.→MEA(1)+HCl (gas); or   (10)Melamine(s)+Cl2(g)+H2O→deacon catalysts→Melamine*HCl(s)+O2(g)   (11)Melamine*HCl→200° C.→Melamine(s)+HCl (g)   (12)The materials should be chosen for their ability to absorb acid gases,e.g. HCl and release it at moderate temperatures, as well as having aresistance to chlorine. The chosen material may either reside in thedeacon reactor or just adjacent to it to shift the equilibrium to theproduction of oxygen.

In a second reactor, as the chlorine reacts with water vapor, the HCland oxygen form. It is important and therefore preferred to run thereaction in the presence of an acid absorbing material that can beregenerated later. This shifts the equilibrium fully to the productionof oxygen. The acid absorbing material is regenerated by heat in aseparate reactor. The use of an HCl absorber is essential to operatingthe Reverse Deacon reaction at a low temperature, and thereby enablingthe entire process to be operated using available and suitable heatsources which are generally at or below 600° C. If there is any residualchlorine (which can be monitored by a chlorine sensor), it can be eitherabsorbed by water if that is the HCl separation medium, or it can bepassed over a much smaller second bed of vanadium chloride II salt. Atlow temperatures (100° C.), Cl₂ will oxidize the vanadium chloride IIback to vanadium chloride III, and the HCl will not react with thevanadium chloride II. This bed can then be periodically regenerated byheating it up to 500° C. to regenerate and recover the Cl₂ and the VCl₂.Other suitable methods will be apparent to the skilled practitioner andmay be employed as well. While such a cleaning step may not benecessary, it does allow for greater design flexibility by putting alower burden on the catalyst operation if needed.

As the HCl is sent back to the first reactor it will generate hydrogengas. Since hydrogen and chlorine react violently, prior to introductionof HCl, the first reactor will have any remaining traces of chlorineremoved either by a vacuum pump or by flushing with the inert gas. Thusonly hydrogen should be present in the out-going gases. At the beginningof the reaction in batch-wise processing, with a large excess of VCl₂available, the hydrogen coming out the reactor (column) should be quitepure. An HCl gas monitor can be placed at or near the output of thecolumn to detect unacceptable HCl levels, and at which point the HClflow would be stopped, the reactor evacuated, and the heat reapplied toregenerate the VCl₃. It is not necessary to react all the VCl₂ sincechlorine generation can be monitored during the heating to ensure thatextra energy is not wasted. If desired, the hydrogen product can also bescrubbed with water or monoethanolamine as described above for oxygencleaning.

Finally, the process can be made continuous by having two reactors withone taking in heat and generating chlorine and the other taking in HCland making hydrogen. This provides a constant flow of gases to thereactor and has various processing advantages. See FIG. 1.

A substantial advantage gained with the V-Process is the avoidance ofthe capital costs required to build a plant with exotic alloys, i.e.costs which mushroom in both material costs and the specialtyfabrications required to work with such materials. By operating at atemperature at or substantially below about 600° C., an importantadvantage is realized, since the industry already has economicalsolutions for handling chlorine and HCl under these rather typicalconditions. Thus, no new engineering or testing is required, and thespecification of materials known to be acceptable over long time periodsfor commercial plants are already well known. Thus, the V-Process allowsfor realistic cost assessments for plant construction, and correspondingrealistic revenue and profit projections, which are essential for anyserious commercial venture.

The V-Process is designed to use the least expensive materialsavailable. There is substantially no loss of the starting materials inthe process. The solids are, for example, vanadium salts that cost about$3-4 per pound of contained vanadium. Since vanadium has an atomicweight of 51 and iodine has an atomic weight of 131, for the same amountof hydrogen produced almost 3 times more iodine is required. Iodinecosts more than 4 times the cost of vanadium, so that the initialcapital cost of chemicals for the prior art I—S process is over 10 timesthose required for the V-Process.

Another advantage that the V-Process has is that unlike the I—S processthe efficiency is not strongly dependent on the input temperature. Inorder even to get to the 40% conversion efficiency with I—S, thetemperatures must be well over 850° C. The high temperature reaction,namely the decomposition of sulfuric acid at over 850° C., leads tocorrosion of the plant materials. Further, iodine is expensive andlosses are a serious problem, and the separation steps are not welldefined and difficult. While the I—S process has been known for over 30years, it has never been practically implemented. The same is true forother high temperature cycles that have been considered.

In the “reverse deacon” step of the V-Process, a catalyst is primarilycopper and cobalt chlorides on an alumina substrate is used. Thesecatalysts are inexpensive and active materials which are readilyavailable commercially. Other suitable catalysts include any materialthat can reversibly accept and give up chlorine. However, in the presentinvention, the uptake of HCl drives the reverse deacon reaction.

Monoethanolamine is also a well-known, inexpensive chemical that isalready cyclically used to remove acidic contaminants from natural gas.Polymers that have an active amine group such as melamine,polyvinyl-pyridine, etc. can also be effectively used, as well as manyother amines or compounds that form HCl salts. Thus the scrubbing andhandling technology is already known and available and practicedeconomically on a very large scale.

The V-Process uses three simple steps that are easily scaled-up to aworking plant. This gives a very high level of confidence in thefinished process. While there seems to be no impediments to theintegration of these steps (separations and other details for this arediscussed above) readily available data will aid in optimizing theprocess, e.g., matching reaction rates and energy inputs. It has beenfound that the initial reaction of V-Process, even without a catalyst,may be initiated at a temperature of below 400° C. See Graphs I and II.

The benefits of using vanadium chloride double salts in the reactioncycle have been discussed above; however, very little data are availableon equilibria in these multicomponent systems at anticipated processingcycle temperatures. In determining thermochemical quantities (e.g.,reaction enthalpy) and kinetic properties for both the hydrogenproduction and chlorine production steps of the process cycle, it isbelieved that for at least two double salts with the general formulaeM₃VCl₆ and M₃VCl₅, where M is an alkali metal ion (e.g., Na or K), theprimary reactions replacing reactions 1 and 3 in the basic cycle are asfollows:2M₃VCl₆=2M₃VCl₅+Cl₂   (13)2M₃VCl₅=2HCl=2M₃VCl₆+H₂   (14)

The preparations of double salts, e.g. using vanadium trichloride havebeen based on fusion of the dry salts (Grena, 1960; Vasilkova andPerfilova, 1965). The sodium and potassium double salts are prepared byfusing stoichiometric mixtures of MCl and VCl₃ according to theliterature. These materials are fully characterized by X-ray diffractionand elemental analysis prior to beginning the reaction studies. In orderto prepare mixed salts under more moderate conditions, and potentiallyin larger quantities, the precipitation of the double salts are obtainedfrom solution. Hydrolysis of VCl₃ is potentially extensive in aqueoussolution, and use of less-hydrolytic solvents (e.g., alcohols) andstrongly acidic solution conditions in making larger samples of thechloride salts are possible.

The design of a practical cyclical process for hydrogen production fromthe thermochemical vanadium cycle utilizes data on the extent and rateof the individual reactions of the cycle. The enthalpies of formation ofthe compounds Na₃VCl₆ and K₃VCl₆ from MCl and VCl₃ have been reported as−25.52 and −60.2 kJ/mol at 298 K, respectively (Vasilkova and Perfilova,1965). While phase-equilibrium data are available for the ternary systemincorporating divalent vanadium chloride (i.e., NaCl—KVCl₃—KCl),thermochemical data for possible double salts (such as KVCl₅) in thedivalent system need to be calculated to provide the extent of reaction(free energy change) for the chlorine-production reaction for thehydrogen-production reaction.

The stoichiometric compounds M₃VCl₅ are believed to be stable comparedto the known coordination compound MVCl₃ in solid solution with MCl.However, since previous studies have focused primarily on phaseequilibria, no kinetic data are presently known that permit estimationof the rates of either reaction. Nevertheless, there are indications inthe literature of instability and/or volatility of some components thatmay potentially restrict the operating range of a practical cycle. Forexample, one reference (Orekhova et al., 1974) suggests that KVCl₃ maybe volatile at high temperatures, and there are indications (Shchukarevand Perfilova, 1963) that the sodium compound Na₃VCl₆ meltsincongruently (i.e., decomposes) at 555° C., near the anticipatedoptimum temperature for the chlorine-production reaction.

Use of a high-temperature flow calorimeter system (Busey et al., 1984)determines simultaneously the rates and thermochemistry of the chlorineand hydrogen-production reactions. In the simplest test for chlorineproduction, the temperature of the calorimeter is raised until both thecalorimeter signal (heat flux) and offgas production indicate the onsetof chlorine production. Capturing the offgas stream for subsequentanalysis indicates the approximate rate and extent of Cl₂ production asa function of the temperature; and full analysis of the offgas streamindicates whether additional volatile products are produced in thereaction. This mode of operation is particularly effective for screeningcompounds and for establishing temperature ranges for further detailedanalysis.

Once the screening studies have been completed for thechlorine-production reaction, detailed information on the rate andextent of this reaction is obtained from steady-state experiments. At aconstant temperature, a constant flow of an inert carrier gas (e.g., N₂)is established through the sample. The calorimetric signal indicates theenthalpy of the chlorine-production reaction, and either on-line(gas-chromatographic) or batch analysis of the offgas stream is used todetermine the rate of the reaction. This mode is particularly effectivefor relatively slow reactions; carrying out these tests over a range oftemperatures establishes optimum kinetic and equilibrium conditions forcycle operation. Once the reaction has been completed at a particulartemperature, as indicated by the disappearance of the thermochemicalsignature of the reaction, the system will be sealed and cooled, and thesample removed for analysis to determine the oxidation state of vanadiumand the state (i.e., crystalline, sintered, or amorphous) of the productsolid.

The hydrogen-production reaction inherently involves both reactant andproduct gas streams. For this reaction the chlorine-depleted solidphase, contained at constant temperatures within the calorimeter workingcall, is exposed to flowing HCl in a carrier gas stream. This gas streamis humidified at varying levels to test the optimum hydrogen-productionreaction. The production of hydrogen is indicated both by analysis ofthe product gas steam and by the measured heat flux arising from theenthalpy of the reaction. However, humidification must be limited so asnot to produce any ox halides of vanadium such as VOCl. Limitingmoisture and keeping the HCl concentration sufficiently high is requiredto accomplish this.

The determination of the steady-state enthalpy of this process, combinedwith knowledge of the rate of reaction from the offgas analysis, enablesone to calculate the enthalpy of formation of the vanadium trichloridedouble salts from MCl and the divalent vanadium chloride. Similarly byobtaining data on the rate of reaction as a function of reactant (HCl)and promoter (H₂) concentrations, total gas pressure, and temperatureone is enabled to optimize the process conditions for thehydrogen-production reaction.

Temperatures required by the V-Process make integration into currentsolar power tower plant designs quite practical. As explained above,operation with solar trough concentrators may also be possible andpractical.

There is great current interest in utilizing coal as a fuel in a cleanand efficient manner. There is also a great and rising demand fornatural gas that is being met by imports, thus increasing the dependencyof the U.S. on foreign sources of energy. The following discloses apreferred application of the V-Process, wherein it is integrated into anintegrated gas combination cycle (IGCC).

The steps used in coal gasification produce large quantities of gases inthe temperature range of 600° to 800° C. or greater. The common practiceis to use these gases to make steam, if it is needed. However, due tothermodynamic limitations, it turns out that it is better to use thesteam in a non-carnot limited chemical process rather than a carrotlimited mechanical process.

The V-Process decomposes water into hydrogen and oxygen with heat inputat the relatively low temperature of about 500° C. This low temperatureis critical to the successful integration of the V-Process into an IGCCprocess.

The first step in an IGCC process is typically to react a carboncontaining source with a certain amount of oxygen and steam at least700° C. or greater. The oxygen is usually pure, but air may also beused. There are two basic reactions taking place in this gasifier.

The first is the reaction of the carbon components with steam; and thesecond is the reaction of carbon components with oxygen, when there isalways a deficit of oxygen so that little if any carbon dioxide isproduced. Nevertheless, carbon monoxide and hydrogen are the desiredproducts as follows.

$\begin{matrix}{\left. {C + {H_{2}O}}\rightarrow{{C\; O} + {H_{2}\mspace{14mu}{DG}}} \right. = {{+ 32}\mspace{14mu}{KCAL}\text{/}{MOLE}}} & (15) \\{\left. {C + {\frac{1}{2}O_{2}}}\rightarrow{C\; O\mspace{14mu}{DG}} \right. = {{- 26}\mspace{14mu}{KCAL}\text{/}{MOLE}}} & (16)\end{matrix}$

Notice that reaction 15 is endothermic and thus requires the input ofenergy and reaction 16 is exothermic and produces energy. Thus it is thegoal of the process to balance these two equations so that the net heatproduced is enough to maintain the reaction and production of CO and H₂.Depending on the content of the feedstock and the other elements presentsuch as bound hydrogen etc. The ratio of the amount of water to oxygenadmitted may vary. Regardless, the temperature of this reactor usuallyneeds to be maintained at least at 700° C. for the reaction to proceedat a reasonable rate. Typically, the gas generated is sent to a gasturbine to be burned to produce electricity. The solids that wouldnormally have to be dealt with in an ordinary boiler, in a baghouse, areinstead removed from the gasifier and disposed of.

The exhaust of the turbine is still at over 500° C. In an IGCC Process,this heat is used to make steam to run a steam turbine to makeadditional electricity. While this step does increase the overallefficiency of the recovery, it is an expensive step relative to usingthat same heat to make hydrogen and oxygen for use in the IGCC Processand thereby increasing the efficiency without having to use a steamturbine at all. With 500° C. steam the steam turbine will only operateat about 18% efficiency. This number was not attractive when energy wascheap. Now that energy is not cheap that number seems more acceptable.However, there are more economical ways to handle that energy. By usingthat energy to split water, both hydrogen and oxygen are produced. Thegasifier requires oxygen to produce a purer higher quality fuel for theturbine. An air separation plant normally supplies this oxygen. Thisplant adds to both the capital costs and the energy consumption of thesystem. However, oxygen from the V-Process eliminates this cost andenergy drain.

The hydrogen can be either used as a fuel or used as a feedstock to makemethane. If the hydrogen is used as a fuel it is simply added to the gasfeed of the gas turbine. These turbines have modified burners to handlehydrogen as a fuel. The burners should be such that they will runproperly on the hydrogen-fuel mixture. Since this fuel is used in placeof the raw gasifier fuel, the output of the turbine will be the same forless fuel consumption, thus increasing the effective efficiency of thesystem. Since the V-Process is over 70% efficient, and the gas turbineis about 32% efficient, the net increase in output is over 22% with farless capital expenditure.

The hydrogen may also be used to make methane through a simplemethanation process with the carbon monoxide as follows:

$\begin{matrix}{\left. {{CO} + {3H_{2}}}\rightarrow{{CH}_{4} + {H_{2}O\mspace{14mu} D\; G}} \right. = {{- 12}\mspace{14mu} K\;{CAL}\text{/}{MOLE}}} & (17)\end{matrix}$

Reaction 17 is exothermic, and runs at about 650° C., and thus this heatmay also be recovered to be used in the V-Process.

Different gasifiers and different feeds result in different amounts ofCO and H₂. However, based on known gasifier technologies, and regardlessof whether the reactor is fluid bed, moving bed, or entrained flow, thehydrogen content tends to be around 14 to 28 (mole) %. The CO contentranges from about 23% to 40%; the CO₂ content ranges from about 6 to 12%and the water is about 6 to 23%. There are also small amounts of methaneproduced (typically under 1%). If air is an oxidant the above numbersare about half of the stated values, since nitrogen makes-up about 50%of the output gas.

According to equation 17 the optimal mix to make methane (based on amole ratio of (CO:H) is 3:1. Gasifiers running on coal requireadditional hydrogen to make methane. Real world fuels such as coal andoil contain anywhere from 6% to 14% hydrogen bound in C—H bonds. Thuswhen these bonds break additional hydrogen is released as shown inreaction 17 and 19 below:(CH₂)_(x)+O₂→XCO+XH₂; and   (18)(CH₂)_(x)+XH₂O→XCO+XH₂.   (19)

Again, similar to reactions 15 & 16 above, reaction 18 which uses oxygenis exothermic and reaction 19 which uses water is endothermic.

Since CO₂ is also a by-product it can be assumed that some of thereactions also produce CO₂. The most likely is the shift reaction asfollows:CO+H₂O→CO₂+H₂.   (20)

Reaction 20 is slightly exothermic under the conditions in the reactor.Also of course some CO can be lost to the more parasitic reaction withoxygen as follows:CO+½O₂→CO₂.   (21)

Reaction 21 is very exothermic. However, under the conditions in thereactor the following reaction is also favored:CO₂+C→2CO   (22)

As can be seen, the complexity of the real reaction system means thatthe net reaction can only be determined by comparing the reactants in,with the products out, including the energy balance.

However reaction 20 (the shift reaction) can be seen as the reactionthat may be eliminated in this system since the CO is needed, and the H₂will come from the V-Process. However, some shifting usually occurs inany gasifier thus accounting for the CO₂ in the output gases. However,depending on the energy and hydrogen balance some CO₂ may be methanatedas well.

IGCC technology is clean. It also converts about 41% of the energy inthe fuel to electricity. But it does this at a cost of over$2,000/kilowatt of electric output. This is almost double the cost of asteam plant, and triple the cost of a gas turbine plant. Further, thegas turbines need to be modified to run on fast burning gases.

An embodiment of the V-Process application will improve this system isto perform a methanation of the gas stream prior to feeding it to thegas turbines to upgrade it. Thus if the stream containing excess CO ispassed over a standard methanation catalyst system, the stream comingout will contain almost no CO and be composed mostly of methane andhydrogen. There would also be water vapor that could be removed ifdesired prior to going to the turbine.

However, the hydrogen component of the steam which has two qualitiesthat are not desired in the gas turbine. The first is that hydrogenlowers the volumetric energy density of the fuel; and the second is thathydrogen increases the flame speed beyond that which is desired. Byeliminating the hydrogen in the fuel, the turbine can burn the fuelusing regular combustion chambers thus lowering the capital costs. Theone drawback to this method is that the methane/CO mixture will haveless energy (by 12 kcal) when burnt as a fuel than the CO/H mixture fromwhich it was made. However, if the mixture is kept hot out of themethanation reactor and fed to the turbine hot the released 12 kcalsshould be recovered in the turbine.

If purification and removal of CO is required any where in the processthere are many selective methods for doing so. One would be to absorbthe CO on a reversible material that can pi-bond to the excess electronpair on the CO. Thus materials such as iron salts or metallic nickel(the Mond process) or metal carbonyls, or complex forming salts such asiron nitrosyl carbonyl can be used as follows:Ni (solid)+4CO (gas)→Ni(CO)₄(BP4OC)   (23)Ni(CO)₄+heat 200° C.→Ni (solid)+4CO (gas).   (24)The 200° C. heat required to release the CO is freely available as wasteheat in the process. Another route is to pass the synthesis gas througha hydrogen separation device. These devices allow part or most of thehydrogen to diffuse through a membrane leaving the fuel mostly CO.

Thus a system where excess coal is available can be constructed. Agasifier can be made to produce enough CO and H₂ for both the productionof electricity and the production of natural gas. The ratio of carbonoxygen and water can be varied to produce the proper ratio of CO to H togive the proper ratio desired for the production of methane and anyleftovers to burn in a gas turbine.

According to FIG. 5, coal is fed into the gasifier (I) with water andoxygen from the V-Process (II). The gases from the gasifier are freed ofparticulate and sulfur compounds (III); the synthesis gas is split inany desired portion between the methanator (IV) and the gas turbine (V).The heat from the gas turbine is supplied to the V-Process (II).Hydrogen from the V-Process is fed to either the turbine or methanereactor as needed along line A. This may also serve to remove any excesshydrogen or CO from the methanator to be delivered to the gas turbine.Other possible applications of the V-Process are discussed below.

There are now thousands of large gas turbines that operate using naturalgas, and that generate electricity. Their efficiency is generally about33%; therefore to generate 1 Mwh of electricity it requires the burningof 3 Mwh of gas. The remaining 2 Mwh is waste heat. Most of this heat iseither not used at all, or used unprofitably. With the V-Process half ofthis or 1 Mwh may be recovered as hydrogen gas, which may either beburned in the turbines (least profitable use) to increase the efficiencyto almost 50%; or the hydrogen and oxygen may be sold. The sale of 25 Kgof H₂ and 200 Kg of O₂ would be worth at least another $40 for each Mwhproduced. The electricity if sold to the local utility would typicallyyield an average of about $35/Mwh, of which typically less than halfwould be profit, or about $15/Mwh. Therefore, incorporating theV-Process with a gas turbine would increase the profitability of theoperation by over 200%. In this application, the V-Process would be inthe form of an add-on module.

Natural gas is now selling at over $5/MMBtu and is slated to do so forthe balance of the decade. (Quotes from the NYMEX May 31, 2004).Government policies have encouraged many large energy users to decide toconsume natural gas. For many years it was below $3. However, the verysuccess of natural gas has started to cause a large rise in its price.While there are methods that can generate natural gas from coal, theytended not to be very competitive at $2-3/MMBtu, and they are also notparticularly energy efficient. Large expenditures are required foroxygen plants so that the methane would not have to be upgraded prior tosale in these older processes. Since the V-Process generates oxygen aswell as hydrogen this expense, in both capital and energy is eliminated.Thereby increasing the efficiency of the process while decreasingcapital costs. With coal costs at about $1/MMBtu there is now asubstantial profit incentive to build a natural gas plant at a coal minewhich would be connected to a pipeline grid. This would eliminate theexpense and energy of hauling coal long distances.

In many oil refineries the crude oils that are process do not havesufficient hydrogen, and therefore, refineries are often net consumersof hydrogen. This market has grown such that merchant hydrogen companieshave built hydrogen plants in areas such as Houston, Tex. where thereare enough refineries to set up a small hydrogen pipeline to servicethem.

However, refiners could reduce the cost of hydrogen even further byusing the V-Process in-house to utilize the many waste heat sources atthe refinery for producing hydrogen gas that would be used in therefinery. Depending on the refinery and the feedstocks, it is possiblethat some or all of the hydrogen needs may be met using the V-Process,with even some excess hydrogen to sell. Where refineries are remote andmerchant hydrogen is more expensive, the V-Process will save even moremoney for the refiner. These cost savings are estimated to be aroundsixty cents to about a dollar per barrel of refined oil. With theaverage crack margin being about $3-$5 this could be a significantimprovement in the refining margin. The process also increases theenergy efficiency of the refinery and therefore makes it moreenvironmentally friendly. Further, all of the current merchant hydrogencomes from steam reformation of natural gas. The high gas pricesmentioned earlier will cause the price of hydrogen to spiral upwards intime. It can be anticipated that in a relative short period of time,nearly one-half of the refiner's margin will be saved by utilizing theV-Process as compared to the continuing to use hydrogen from naturalgas.

The least expensive operationally and environmentally friendly way togenerate hydrogen is using solar generation processes in which there isno fuel consumption. Solar energy is collected with large mirrors orholographic optical components. These components are less expensive thanthe photovoltaic cells that generate electricity at about 14%efficiency. Optical components concentrate sunlight up to about 500° C.at over 80% efficiency. This energy when utilized in the V-Process at60% efficiency produces large quantities of hydrogen gas with lowcapital costs at 48% efficiency. If the electricity produced by thephotocell were used to electrolyze water, only 12% efficacy would berealized. For a solar farm of similar size, the V-Process not onlyproduces four times the hydrogen gas, but the capital cost of the solarfarm is one 1/10 of the cost associated with the photovoltaic method.

At these prices and efficiencies the capital cost is about 70 cents perkilowatt which when amortized over 30 years (assuming 2,880 useablehours of sun per year) results in a cost of less than 1 cent perkilogram of hydrogen. Since the energy is free, and nine kilograms ofwater (a bit over 2 gallons) costs less than a penny, the overall costfor the hydrogen will be pennies per kilogram, while its value will beabout a dollar per kilogram.

The V-Process may be installed wherever hydrogen is needed. Further,large solar farms are now an economic reality and can generate asignificant portion of the energy requirements of the country. Desertland or any other place with a large solar resource can be expected togenerate more than $20,000 per acre per year of hydrogen if theV-Process is utilized. This is far more income than could be generatedby using the land for agricultural purposes.

As a direct outgrowth of the present invention, it has been recognizedthat hydrogen chloride is a by-product of many chemical processes. Suchprocesses include the chlorination of many organic compounds thatprovide us many useful polymers. Such processes have the generalreaction RH+Cl₂. As can be seen, half the chlorine value is lost in theHCl. It would be economically and environmentally very favorable torecover this chlorine in the HCl for reuse, and thus increase thechlorine utilization by a factor of two. The energy generation ofchlorine from salt is an energy intensive process. While in theV-Process the HCl is used to recycle VCl₂ to VCl₃, there is often no usefor the hydrogen chloride by-product. Further, the chlorine value in thehydrogen chloride often represents one-half of the chlorine used, andthus would be of value if it could be recovered in the form of chlorinefor reuse on-site. This would also be true in the case of other halogengases such as bromine and iodine derived from splitting HBr and HI,respectively.

Two known methods for splitting HCl are the so-called “Deacon Process”and electrolysis. Electrolysis simply dissolves the HCl in water andrecovers chlorine at an anode and hydrogen at a cathode as follows:HCl→e−→½H₂+½Cl₂.   (25)The process is costly from both a capital and operational point of viewand is not practiced.

The Deacon Process oxidizes HCl with air and is as follows:2HCl+½O₂→catalyst→Cl₂+H₂O   (26)While this process is practiced, wet Cl₂ is quite corrosive and adds tomaintenance costs. Another problem is that hydrogen is not recovered andmany sites could use the hydrogen. Again the Deacon Process is anequilibrium process and is thus not widely used.

What is disclosed hereinbelow is a novel process that uses thedecomposition of a metal halide which must be able to be decomposed andgive off a halogen gas at a reasonable temperature. The initial step ofthe V-Process is one example. The metal of the remaining lower valencemetal halide (or metal) must then be able to react with HCl to give offhydrogen and regenerate the original compound. Again, the third step ofthe V-Process is one example. Accordingly, a generic formula is asfollows:MClx→heat→MCly+(x−y)/2 Cl (where x>y)   (27)MCly+(x−y)HCl→heat→MClx+(x−y)/2 H₂; and   (28)Results in a net equation as shown in reaction (29) below:HCl+heat→½H₂+½Cl₂.   (29)FeCl₃→heat>285° C.→FeCl₂+½Cl₂   (30)FeCl₂+HCl→heat→FeCl₃+½H₂.   (31)Note that reactions (30) and (31) above net out to the same as reaction(29).VCl₃→heat→500° C.→VCl₂+½Cl₂   (32)VCl₂+HCl→heat→VCl₃+½H₂.   (33)Again, reactions (32) and (33) net out to reaction (29). However,reaction (32) proceeds through an intermediate of VCl₄. To prevent this,double salts may be used such as below:NaVCl₄→NaVCl₃+½Cl₂   (34)NaVCl₃+HCl→NaVCl₄+½H₂.   (35)Further, catalysts that help the release of chlorine may also be useful.For instance FeCl₃ does catalyze the decomposition of VCl₄, thusFeCl₃→FeCl₂+½Cl₂ at only 285° C.   (36)But reaction (33) takes place instantly. FeCl₂+VCl₄→FeCl₃+VCl₃.   (37)Thus, the net reaction (34) below takes place more rapidly at 285° C.than would pure VCl₄. VCl₄→VCl₃+½Cl₂ is faster at 285° C. with FeClxthan without.   (38)Other materials that decompose to chlorine can also be used such asPCl₅→PCl₃+Cl₂.   (39)

In general the higher oxidation states of elements with more than onecommon oxidation state will tend to give off chlorine when heated and besuitable as a catalyst or the main material in this process. Otherexamples of this are as follows:PbCl₄→PbCl₂+Cl₂   (40)SbCl₅→SbCl₃+Cl₂   (41)CrCl₄→CrCl₃+½Cl₂   (42)MnCl₄→MnCl₂+Cl₂   (43)CoCl₃→CoCl₂+½Cl₂   (44)KNiCl₄→KNiCl₃+½Cl₂   (45)NiCl₃→NiCl₂+½Cl₂   (46)BiCl₅→BiCl₃+½Cl₂   (47)

Many other combinations will be obvious to those skilled in the art. Themost useful compounds will be those such that the lower valence state isof sufficient reducing power to reduce hydrogen from HCl. These lowervalence compounds are V₂+, Cr₂+, Fe₂+, P₃+, etc.

A facility that generates hydrogen chloride may easily use waste heat orintentionally generate the heat to recover both hydrogen and chlorinevalues from hydrogen chloride. Such a process will reduce the chlorineconsumption in half, save energy and eliminate a waste stream. Manyvariations of the foregoing invention will be apparent to those skilledin the art, accordingly, the teachings of the present invention is notto be understood as limited to the specific processes and formulae,equations, temperatures, materials disclosed herein, which are primarilyadvanced by way of example.

1. A process for producing hydrogen comprising: decomposing a metal halide compound MX using heat and in the presence of a catalyst so as to reduce the metal M in the metal halide compound MX from an initial valence state to a lower valence state; wherein a gas is formed, thereafter, the gas is reacted with water in the presence of an acid-absorbing material to form oxygen and an acidic compound, the acidic compound being formed by an acid and the acid absorbing material; separating the oxygen; separating the acid from the acid-absorbing material; and reacting the acid and the reduced metal halide to produce hydrogen and the compound MX, wherein the metal halide compound MX is vanadium trichloride, and wherein the catalyst is capable of lowering the decomposition temperature of vanadium trichloride.
 2. A process according to claim 1 wherein the process is a dry process.
 3. The process according to claim 1 wherein at least one of the reactions is a wet reaction.
 4. The process according to claim 1 wherein the catalyst is selected from the group consisting of PbCl₄, SbCl₅, CrCl₄, MnCl₄, CoCl₃, KNiC1 ₄, NiCl₃, BiCl₅, FeCl₃, and CuCl₂.
 5. The process according to claim 1, wherein the catalyst is FeCl₃.
 6. The process according to claim 1 operated as a batch process.
 7. The process according to claim 1 operated as a continuous process.
 8. The process according to claim 1 wherein the heat used in all reactions is at a temperature equal to or lower than the temperature of the heat used in reducing MX to a lower valence state.
 9. The process according to claim 8 wherein the heat used in all reactions is about 600° C. and below.
 10. The process according to claim 9 wherein the heat used in reducing MX to a lower valence state is about 400° C. and below.
 11. The process according to claim 1, wherein the acid-absorbing material is capable of being regenerated by heat.
 12. The process according to claim 11 wherein the acid-absorbing material is selected from the group consisting of a polymer having an active amine group, amines, and compounds that form a hydrogen halide salt.
 13. The process according to claim 11 wherein the acid-absorbing material is selected from the group consisting of monoethanolamine, diethanolamne, triethonolamine, melamine, zeolites, charcoals, silicas, alumina, magnesia and compounds that have any functionality that can reversibly absorb acid gas.
 14. The process according to claim 1 wherein a catalyst is used in reacting the gas with water and acid-absorbing material.
 15. The process according to claim 14 wherein the catalyst is selected from the group consisting of a cobalt catalyst and a copper catalyst.
 16. The process according to claim 1, wherein solar power is used as a source of heat for at least one of the reactions.
 17. The process according to claim 1, wherein a source of heat for at least one of the reactions is selected from the group consisting of exhaust from a gas turbine, flue gases, waste heat from any chemical reactions where heat is available, foundry cooling processes, burning of off-gases from a refinery, and oil and natural gas well, intentional burning of lower BTU gases which produce a lower flame temperature than pure fuels, and the burning of any fuels for the purpose of generating hydrogen and oxygen.
 18. The process according to claim 1, further comprising feeding the produced hydrogen into an integrated gas combination cycle.
 19. The process according to claim 1, further comprising feeding the produced hydrogen into a gas turbine to generate electricity.
 20. The process according to claim 1, further comprising feeding the produced hydrogen into a process for generating natural gas from coal.
 21. The process according to claim 1 further comprising feeding the produced hydrogen into a process for refining crude oil.
 22. The process according to claim 1, wherein the heat used in all reactions is at a temperature of about 600° C. and below.
 23. The process according to claim 1, wherein the heat used in reacting the starting metal halide is at a temperature of about 400° C. and below.
 24. A process for producing hydrogen comprising: decomposing a metal halide compound MX using heat and in the presence of a catalyst so as to reduce the metal M in the metal halide compound MX from an initial valence state to a lower valence state; wherein a gas is formed, thereafter, the gas is reacted with water in the presence of an acid-absorbing material to form oxygen and an acidic compound, the acidic compound being formed by an acid and the acid absorbing material; separating the oxygen; separating the acid from the acid-absorbing material; and reacting the acid and the reduced metal halide to produce hydrogen and the compound MX, wherein the catalyst is capable of lowering the decomposition temperature of the metal halide compound MX, and wherein M is selected from the group consisting of vanadium, chromium, niobium, titanium, molybdenum, manganese and iron.
 25. The process according to claim 24 wherein X is selected from the group consisting of chlorine, bromine and iodine.
 26. The process according to claim 24 wherein MX is in the form of a double salt comprising a second salt.
 27. The process according to claim 26 wherein a first portion of the second salt forming the double salt is selected from the group consisting of sodium, potassium, vanadium, chromium, niobium, titanium, molybdenum, manganese, iron and is different than M; and wherein a second portion of the second salt forming the double salt is selected from the group consisting of chlorine, bromide and iodine and is the same as X. 